Composite materials are typically comprised of a matrix of orientated fibrous material such as graphite, boron, glass, polyimides (e.g. Kevlar), and the like impregnated with an epoxy, polymeric, phenolic or other similar organic resinous material. The use of composite materials to manufacture composite articles, especially in the aerospace industry where the strength/weight ratio of composite materials provides a significant advantage over conventional materials, is on the upswing.
Composite material manufacturing systems and processes may be characterized by the nature of the composite material utilized in the system or process. Such systems or processes are generally characterized as either "prepreg" or "wet resin" systems or processes. Prepreg systems or processes utilize composite materials that are formed by impregnating woven fibrous cloth, yarn, or fiber tow with a predetermined amount of organic resin, and staging and drying the organic resin to form a partially cured ("tacky") composite material (prepreg), which is subsequently packaged in protective film. Prepreg composite material in the tacky condition is handled and processed in all the operations comprising the pre-cure fabrication phase. Wet resin systems or processes such as resin transfer molding or vacuum bagging, in contrast, utilize only the orientated fibrous material matrix in the pre-cure fabrication phase. Organic resin is injected into the orientated fibrous material matrix immediately prior to the initiation of the cure fabrication phase. Prepreg and wet resin manufacturing systems or processes each have distinct advantages and disadvantages in the manufacture of composite articles.
Composite articles may be fabricated utilizing a plurality of stacked, preimpregnated fiber plies which vary in size, shape and fiber matrix orientation. The pre-cure fabrication phase in forming composite articles typically involves several independent operations such as cutting of prepreg composite material into individual prepreg composite plies having the requisite shape, stacking or placing the cut prepreg composite plies in the mold cavity in accordance with the desired fiber orientation (layup), and forming each stacked prepreg composite ply over a mold surface contour to ensure proper compaction (debulking) of stacked prepreg composite plies, e.g., without wrinkling, during curing.
Prior art pre-cure fabrication operations are typically highly labor intensive and time consuming (and thus costly), requiring manual handling of the prepreg composite material/plies during the operations of the pre-cure fabrication phase. For example, the prepreg composite material workpiece or roll generally must be hand-placed into position, cut along guide lines to the desired shape or pattern (configuration), and hand transported to a molding station or cell where the cut prepreg composite ply is hand laid or stacked in a mold cavity. Hand pressure is utilized to conform the stacked prepreg composite ply to the mold surface contour and to tack prepreg composite plies in combination with previously stacked plies. Each prepreg composite ply typically is encased within a protective film material, which facilitates handling of individual prepreg composite plies by protecting the prepreg composite plies from contamination or sticking during handling, that must be manually removed prior to stacking of subsequent prepreg composite plies.
Various attempts have been made to reduce the adverse effects of the labor intensive operations involved in pre-cure processing of preimpregnated composite materials. Electronically controllable suction devices have been utilized for automatic handling of preimpregnated composite materials, with limited success. Such devices were configured and/or operative to match a particular prepreg ply configuration, which limited the flexibility of such devices to a single operational set-up. In addition, such devices did not readily accommodate prepreg ply configurations of exotic configuration, i.e., elaborate contours, holes, etc., of the type typically encountered in aerospace manufacturing applications. Ply transfer cycles, and inspection of ply configuration and location, was generally limited to a single ply per cycle which increased overall processing time.
Some limited success has been achieved in developing an integrated, automated system for cutting preimpregnated composite materials. Such a system automatically dispenses and cuts prepreg composite material utilizing a numerically controlled cutting machine. Cut plies are individually transferred, sans protective films, to a magazine based handling system. A loaded magazine, which constituted a kit of plies, was then delivered by conventional transfer means to a layup or stacking station or cell.
There does not appear to have been any successful attempt to develop a composite material system for pre-cure processing operations wherein the individual operations comprising the pre-cure processing phase were fully automated and integrated with one another. A need exists for an integrated, automatic composite material manufacturing system and method for pre-cure processing of preimpregnated composite materials. Such a system should provide efficient automatic handling of preimpregnated composite materials or plies during all of the operations of the pre-cure processing phase and during any transfers between operations. Furthermore, the system should be integrated so that there is synchronization between the various automated pre-cure processing operations such as cutting, unloading, layup, and forming as well as any intermediate automated handling steps. In addition, the integrated, automated composite material manufacturing system should provide a high degree of quality and repeatability.
Such a system requires an automated material handling apparatus that is capable of automatic handling of preimpregnated composite materials in a reliable, consistent, and efficient manner. Due to the "tacky" nature of preimpregnated composite materials, prior art material handling apparatus utilizing vacuum forces have not proven reliable for automated handling operations involving preimpregnated composite materials. The vacuum forces generated by such prior art material handling apparatus have generally proven sufficient to pickup and retain preimpregnated composite materials in combination with the material handling apparatus.
However, upon termination of the vacuum forces for placement of preimpregnated composite materials, it has been noted that such prior art material handling apparatus did not consistently and reliably release such composite materials. To alleviate this problem, prior art material handling apparatus were modified to apply a positive pressure force against the preimpregnated composite material to disengage such composite material from the handling apparatus. It was found, however, that positive pressure forces applied directly against the preimpregnated composite materials held in combination by the material handling apparatus did not operate as a suitable disengagement mechanism
Low magnitude positive pressure forces were not effective in consistently and reliably disengaging preimpregnated composite materials from the material handling apparatus. Large magnitude positive pressure forces, in contrast, while generally sufficient to disengage preimpregnated composite materials from the material handling apparatus, tended to induce displacement errors in the spatial placement positions of the released composite materials, a significant disadvantage in automated composite material manufacturing systems and methods. Complicating the process of determining the proper magnitude for the positive pressure forces for a material handling apparatus is the fact that the "tackiness" of preimpregnated composite materials varies, depending upon a variety of factors such as the shape of the preimpregnated composite material to be handled and the type of organic resin utilized.
A need exists for a material handling apparatus that is capable of automated handling of preimpregnated composite materials in a reliable, consistent, and efficient manner. The material handling apparatus should be capable of automated handling of preimpregnated composite materials of varying sizes and of varying shapes or patterns. The material handling apparatus should be capable of being readily integrated into an automated composite material manufacturing system and method.